In recent years, high-speed internet service called fiber to the home (FTTH) has been widely utilized in which optical fibers are brought into homes. Since FTTH systems require indoor wiring, a need exists for optical fibers which can accommodate small bend diameters.
For example, PATENT DOCUMENT 1 describes an optical fiber including a centrally located core, a first cladding layer surrounding the core, a second cladding layer surrounding the first cladding layer, and a third cladding layer surrounding the second cladding layer. The highest refractive index of the core is higher than each of the highest refractive indices of the first, second, and third cladding layers. The highest refractive index of the second cladding layer is lower than each of the highest refractive indices of the first and third cladding layers. When the core radius is a1, and the radius of the outer circumference of the first cladding layer is a2, the value a2/a1 is greater than or equal to 2.5 and less than or equal to 4.5. When the refractive index of the third cladding layer is used as a reference, the relative refractive index difference between the core and the third cladding layer is greater than or equal to 0.20% and less than or equal to 0.70%. The refractive index volume V of the second cladding layer defined by a predetermined equation corresponding to the equation below is greater than or equal to 25%μm2 and less than or equal to 110% μm2. PATENT DOCUMENT 1 further describes that the optical fiber has a low bending loss and good connectivity with a general transmission optical fiber and can be manufactured at low cost.    PATENT DOCUMENT 1: Japanese Patent No. 3853833